/**
* This class handles LZW encoding
* Adapted from Jef Poskanzer's Java port by way of J. M. G. Elliott.
* @author Kevin Weiner (original Java version - kweiner@fmsware.com)
* @author Thibault Imbert (AS3 version - bytearray.org)
* @version 0.1 AS3 implementation
*/

  //import flash.utils.ByteArray;

  LZWEncoder = function()
  {
      var exports = {};
    /*private_static*/ var EOF/*int*/ = -1;
    /*private*/ var imgW/*int*/;
    /*private*/ var imgH/*int*/
    /*private*/ var pixAry/*ByteArray*/;
    /*private*/ var initCodeSize/*int*/;
    /*private*/ var remaining/*int*/;
    /*private*/ var curPixel/*int*/;

    // GIFCOMPR.C - GIF Image compression routines
    // Lempel-Ziv compression based on 'compress'. GIF modifications by
    // David Rowley (mgardi@watdcsu.waterloo.edu)
    // General DEFINEs

    /*private_static*/ var BITS/*int*/ = 12;
    /*private_static*/ var HSIZE/*int*/ = 5003; // 80% occupancy

    // GIF Image compression - modified 'compress'
    // Based on: compress.c - File compression ala IEEE Computer, June 1984.
    // By Authors: Spencer W. Thomas (decvax!harpo!utah-cs!utah-gr!thomas)
    // Jim McKie (decvax!mcvax!jim)
    // Steve Davies (decvax!vax135!petsd!peora!srd)
    // Ken Turkowski (decvax!decwrl!turtlevax!ken)
    // James A. Woods (decvax!ihnp4!ames!jaw)
    // Joe Orost (decvax!vax135!petsd!joe)

    /*private*/ var n_bits/*int*/ // number of bits/code
    /*private*/ var maxbits/*int*/ = BITS; // user settable max # bits/code
    /*private*/ var maxcode/*int*/ // maximum code, given n_bits
    /*private*/ var maxmaxcode/*int*/ = 1 << BITS; // should NEVER generate this code
    /*private*/ var htab/*Array*/ = new Array;
    /*private*/ var codetab/*Array*/ = new Array;
    /*private*/ var hsize/*int*/ = HSIZE; // for dynamic table sizing
    /*private*/ var free_ent/*int*/ = 0; // first unused entry

    // block compression parameters -- after all codes are used up,
    // and compression rate changes, start over.

    /*private*/ var clear_flg/*Boolean*/ = false;

    // Algorithm: use open addressing double hashing (no chaining) on the
    // prefix code / next character combination. We do a variant of Knuth's
    // algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
    // secondary probe. Here, the modular division first probe is gives way
    // to a faster exclusive-or manipulation. Also do block compression with
    // an adaptive reset, whereby the code table is cleared when the compression
    // ratio decreases, but after the table fills. The variable-length output
    // codes are re-sized at this point, and a special CLEAR code is generated
    // for the decompressor. Late addition: construct the table according to
    // file size for noticeable speed improvement on small files. Please direct
    // questions about this implementation to ames!jaw.

    /*private*/ var g_init_bits/*int*/;
    /*private*/ var ClearCode/*int*/;
    /*private*/ var EOFCode/*int*/;

    // output
    // Output the given code.
    // Inputs:
    // code: A n_bits-bit integer. If == -1, then EOF. This assumes
    // that n_bits =< wordsize - 1.
    // Outputs:
    // Outputs code to the file.
    // Assumptions:
    // Chars are 8 bits long.
    // Algorithm:
    // Maintain a BITS character long buffer (so that 8 codes will
    // fit in it exactly). Use the VAX insv instruction to insert each
    // code in turn. When the buffer fills up empty it and start over.

    /*private*/ var cur_accum/*int*/ = 0;
    /*private*/ var cur_bits/*int*/ = 0;
    /*private*/ var masks/*Array*/ = [ 0x0000, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF, 0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF ];

    // Number of characters so far in this 'packet'
    /*private*/ var a_count/*int*/;

    // Define the storage for the packet accumulator
    /*private*/ var accum/*ByteArray*/ = [];

    var LZWEncoder = exports.LZWEncoder = function LZWEncoder (width/*int*/, height/*int*/, pixels/*ByteArray*/, color_depth/*int*/)
    {

      imgW = width;
      imgH = height;
      pixAry = pixels;
      initCodeSize = Math.max(2, color_depth);

    }

    // Add a character to the end of the current packet, and if it is 254
    // characters, flush the packet to disk.
    var char_out = function char_out(c/*Number*/, outs/*ByteArray*/)/*void*/
    {
      accum[a_count++] = c;
      if (a_count >= 254) flush_char(outs);

    }

    // Clear out the hash table
    // table clear for block compress

    var cl_block = function cl_block(outs/*ByteArray*/)/*void*/
    {

      cl_hash(hsize);
      free_ent = ClearCode + 2;
      clear_flg = true;
      output(ClearCode, outs);

    }

    // reset code table
    var cl_hash = function cl_hash(hsize/*int*/)/*void*/
    {

      for (var i/*int*/ = 0; i < hsize; ++i) htab[i] = -1;

    }

    var compress = exports.compress = function compress(init_bits/*int*/, outs/*ByteArray*/)/*void*/

    {
      var fcode/*int*/;
      var i/*int*/ /* = 0 */;
      var c/*int*/;
      var ent/*int*/;
      var disp/*int*/;
      var hsize_reg/*int*/;
      var hshift/*int*/;

      // Set up the globals: g_init_bits - initial number of bits
      g_init_bits = init_bits;

      // Set up the necessary values
      clear_flg = false;
      n_bits = g_init_bits;
      maxcode = MAXCODE(n_bits);

      ClearCode = 1 << (init_bits - 1);
      EOFCode = ClearCode + 1;
      free_ent = ClearCode + 2;

      a_count = 0; // clear packet

      ent = nextPixel();

      hshift = 0;
      for (fcode = hsize; fcode < 65536; fcode *= 2)
        ++hshift;
      hshift = 8 - hshift; // set hash code range bound

      hsize_reg = hsize;
      cl_hash(hsize_reg); // clear hash table

      output(ClearCode, outs);

      outer_loop: while ((c = nextPixel()) != EOF)

      {

        fcode = (c << maxbits) + ent;
        i = (c << hshift) ^ ent; // xor hashing

        if (htab[i] == fcode)
        {
        ent = codetab[i];
        continue;
        } else if (htab[i] >= 0) // non-empty slot
        {
          disp = hsize_reg - i; // secondary hash (after G. Knott)
          if (i == 0)
          disp = 1;
          do
          {

            if ((i -= disp) < 0) i += hsize_reg;

            if (htab[i] == fcode)
            {
            ent = codetab[i];
            continue outer_loop;
            }
          } while (htab[i] >= 0);
        }

        output(ent, outs);
        ent = c;
        if (free_ent < maxmaxcode)
        {
          codetab[i] = free_ent++; // code -> hashtable
          htab[i] = fcode;
        } else cl_block(outs);
      }

      // Put out the final code.
      output(ent, outs);
      output(EOFCode, outs);

    }

    // ----------------------------------------------------------------------------
    var encode = exports.encode = function encode(os/*ByteArray*/)/*void*/
    {
      os.writeByte(initCodeSize); // write "initial code size" byte
      remaining = imgW * imgH; // reset navigation variables
      curPixel = 0;
      compress(initCodeSize + 1, os); // compress and write the pixel data
      os.writeByte(0); // write block terminator

    }

    // Flush the packet to disk, and reset the accumulator
    var flush_char = function flush_char(outs/*ByteArray*/)/*void*/
    {

      if (a_count > 0)
      {
        outs.writeByte(a_count);
        outs.writeBytes(accum, 0, a_count);
        a_count = 0;
      }

    }

    var MAXCODE = function MAXCODE(n_bits/*int*/)/*int*/
    {

      return (1 << n_bits) - 1;

    }

    // ----------------------------------------------------------------------------
    // Return the next pixel from the image
    // ----------------------------------------------------------------------------

    var nextPixel = function nextPixel()/*int*/
    {

      if (remaining == 0) return EOF;

      --remaining;

      var pix/*Number*/ = pixAry[curPixel++];

      return pix & 0xff;

    }

    var output = function output(code/*int*/, outs/*ByteArray*/)/*void*/

    {
      cur_accum &= masks[cur_bits];

      if (cur_bits > 0) cur_accum |= (code << cur_bits);
      else cur_accum = code;

      cur_bits += n_bits;

      while (cur_bits >= 8)

      {

        char_out((cur_accum & 0xff), outs);
        cur_accum >>= 8;
        cur_bits -= 8;

      }

      // If the next entry is going to be too big for the code size,
      // then increase it, if possible.

      if (free_ent > maxcode || clear_flg)
      {

        if (clear_flg)
        {

          maxcode = MAXCODE(n_bits = g_init_bits);
          clear_flg = false;

        } else
        {

          ++n_bits;

          if (n_bits == maxbits) maxcode = maxmaxcode;

          else maxcode = MAXCODE(n_bits);

        }

      }

      if (code == EOFCode)
      {

        // At EOF, write the rest of the buffer.
        while (cur_bits > 0)
        {

          char_out((cur_accum & 0xff), outs);
          cur_accum >>= 8;
          cur_bits -= 8;
        }


        flush_char(outs);

      }

    }
    LZWEncoder.apply(this, arguments);
     return exports;
  }
